Production of flat metal sheets



1966 R. 0. STEIGERWALT 3,233,085

PRODUCTION OF FLAT METAL SHEETS Filed April 9, 1964 INVENTOR. ROBE]? T0. STE/GERWALT @MM M Attorney United States Patent ()fiice 3,236,086Patented Feb. 22, 1966 3,236,086 PRODUCTION GF FLAT METAL SHEETS RobertD. Steigerwalt, Pittsburgh, Pa, assignor to United States SteelCorporation, a corporation of Delaware Filed Apr. 9, 1964, Ser. No.358,587 1 Claim. (Cl. 72-296) This application relates to the productionof large metal sheets and more particularly to stretcher levelling largesteel sheets.

Metal sheet material formed of steel and the like is conventionallyflattened or levelled by roller levelling or stretcher levelling. In theformer, the sheet or strip material is run through a series of rollersdisposed to bend the material in alternate directions and achieve aflattened condition. This is generally applied to strip material but dueto the necessity of using rather small diameter rolls is limited to thewidth of material that can be handled. Stretcher levelling is the methodmost generally used for flattening plates and is applicable to theheavier sheet gauges. However, large, lighter sheet gauges, i.e. thosehaving a length/ thickness ratio in excess of 3000 cannot be stretcherlevelled because stretching produces a wavy out-of-flat condition.

Accordingly, it is an object of this invention to provide a method offlattening large, light gauge sheets.

The foregoing and further objects will be apparent from the followingspecification when read in conjunction with the attached drawing,wherein:

FIGURE 1 is an isometric view of an assembly of sheets to bestraightened and cover plates therefor, partially broken away to showthe interior of the pack;

FIGURE 2 is a side view showing the combined flattening and stretchingoperation of my invention; and

FIGURE 3 is a view similar to FIGURE 1 of a modification.

Referring more particularly to the drawing, the letter P denotes asandwich or pack composed of outer or cover plates 2 and inner sheets 4to be stretcher levelled. Preferably the cover plates have a thicknessgreater than that of the sheets and preferably at least 5 times that ofthe sheets. Generally the inner sheets are composed of high yieldstrength steel and are of large size such as 12 feet or more in lengthand less than .04" gauge thereby having a length/ thickness ratio inexcess of 3000.

In FIGURE 2, the pack P is shown disposed between platens 12 with theends of the pack extending outwardly therebeyond a sufiicient distanceto be gripped by grips 20 of a conventional hydraulically operatedstretcher levelling machine.

Due to heat treatment, the sheets of the pack are considerably distortedso that preliminary to the stretching operation, pressure may be appliedto the platens by a suitable press to partially straighten the sheetsand substantially remove warpage therefrom. The warpage results in thesheets being longer on one side than the other and such distortion isremoved by the preliminary pressing to prevent one side being stretchedmore than the other in subsequent stretcher levelling. Such pressing maybe applied to the sheets individually or to the pack.

After pressing, the grips 20 are operated to grip the sheets and thecover plates, and tension applied to the assembly to stretch the sheetsand cover plates beyond the yield point of the material. The pressure ofthe cover plates, which may be augmented by the platens, preventsrippling or furrowing of the sheets during stretching so that acompletely flattened condition is obtained. The tension may be appliedwhile the pack or assembly is below, at or above room temperature butbelow the critical temperature.

In one application of the invention, the pack P may be assembled priorto rolling to final gauge. In this form the pack will have side bars Bsurrounding the inner sheets 4 of difiicult to roll material. The sidebars are welded to the cover plates 2 to form a unitary assembly. Thecover plates have a lower yield strength than the inner sheets 4.Following rolling to produce large size sheets and thereafter heating todevelop the required physical properties, the assembly is quitedistorted and warped and should be stretched as described in connectionwith the foregoing assembly of sheets and cover plates to flatten theinner sheets. The grips 20 of the stretcher leveller exert force on thetop and bottom cover plates of the pack. The inner sheets between thecover plates are gripped by frictional forces exerted through the coverplates. During stretching, horizontal forces are applied stretching thepack past the yield point of the members until a permanent set andflatness is obtained. Due to the lower yield strength thereof, the coverplates stretch first. Also transverse forces are set up during thestretching operation along with the frictional forces resulting from thecover plates stretching before the inner sheets. These forces combine toprevent the formation of the wavy out-of-flat condition normallyresulting from stretching sheets having a length/thickness ratio inexcess of 3000.

This is a continuation-in-part of my copending application Ser. No.39,542, filed June 29, 1960 and now Patent No. 3,152,383, issued on Oct.13, 1964.

While I have shown and described certain specific embodiments of myinvention, it will be understood that these embodiments are merely forthe purpose of illustration and description and that various other formsmay be devised within the scope of my invention as defined in theappended claim.

I claim:

A method of producing large flat heat-treated sheets havinglength/thickness ratio in excess of 3000 comprising forming a pack ofsheets having said length/ thickness ratio, said pack having coverplates on both sides thereof having a lower yield strength than thesheets of said pack, and stretching said pack and cover plates beyondthe yield point of the sheets of the pack and of the cover plateswhereby large flat sheets are obtained.

References Cited by the Examiner UNITED STATES PATENTS 1,811,599 6/1931Thomas.

2,693,637 11/1954 Peabody et a1. 15335 XR 2,961,028 11/1960 Bath 153353,018,817 1/1962 Wheeler et al. 15335 3,066,384 12/1962 Heger 153-86 XRCHARLES W. LANHAM, Primary Examiner.

JOHN F. CAMPBELL, Examiner.

